Regeneration of chemical plating baths



United States Patent 3,340,073 REGENERATION OF CHEMICAL PLATING BATHS Eberhard Zirngiebl, Cologue-Flittard, and Heinz-Giiuter Klein, Cologne-Deutz, Germany, assignors to Farbeufabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Continuation of application Ser. No. 196,901, May 23, 1962. This application Dec. 2, 1966, Ser. No. 599,344 Claims priority, application Germany, May 27, 1961, F 34,032 8 Claims. (Cl. 1061) This application is a continuation of application Ser. No. 196,901, filed May 23, 196-2.

Chemical plating baths are known which contain as a reducing agent boron hydrides with one to four hydrogen atoms linked directly to boron. These baths work at a satisfactory plating rate and reduction yield until about 75% of the nickel applied has been withdrawn from the bath by plating. The reduction yield and plating rate then decrease considerably whereupon a further use of the bath becomes uneconomical.

The investigation of the plating process has shown that the increasing content of alkali metal borate and alkali metal chloride in the baths leads to a deterioration of the reduction yields and a decrease in the plating rate, possibly even to the stopping of the plating process. This action of the above mentioned alkali metal salts makes it also impossible to regenerate used baths, in a simple manner, by adding salts of the metals to be deposited. In addition, the high content of the used plating baths of alkali metal hydroxide (about 1 mol per litre) causes the precipitation of heavy metal hydroxide which is then reduced to the metal by the reducing agent still present in the bath. The precipitates thus formed are difficult to filter, and metal residues still present in the plating bath, acting as decomposition catalysts, result in, on addition of boron hydrides with one to four hydrogen atoms directly linked to boron, the spontaneous decomposition 40 of the baths.

The object of the invention is to provide a process for the regeneration of chemical plating baths, containing as a reducing agent boron hydrides with one to four hydrogen atoms directly linked to boron, characterised by reacting the used baths with water-soluble alkaline earth metal compounds, preferably with magnesium chloride, and filtering off the precipitates thereby formed. The filtrates are then treated once more with the salt of the plating metal and a complex former or reducing agent. The working up can be carried out with alkaline earth metal compounds in the solid state or in solution.

Giving details, it was found that by the addition of a suitable quantity of watersoluble alkaline earth metal compounds to the used alkaline plating baths (1) the alkali metal borate is precipitated practically quantitatively,

(2) the OH-ions are removed from the plating baths,

(3) the content of alkali metal salt is brought to a constant value, 60 (4) losses of plating metal salt and complex former are very small.

In a hundred hours experiment there was analyzed a constant alkali metal salt content of the plating baths. This astonishing effect is perhaps caused by a carry down 65 of NaCl with the other components of the precipitation. Subsequent to the removal of the interfering components a simple freshening up of the baths with metal salt or metal salt solution is possible. The baths thus treated 7 possess the same reduction yield and plating rate as freshly prepared compositions.

Similarly, with chemical plating baths not containing any alkali metal hydroxide (for example plating baths containing ammonia as a complex former), the addition of a water-soluble alkaline earth metal compound causes the removal of alkali metal borate which interfered with the plating process.

Suitable water-soluble alkaline earth metal compounds according to the invention are, for example, magnesium chloride, magnesium sulphate, magnesium acetate, calcium chloride, strontium chloride, barium chloride.

The working up of the used chemical plating baths working only at a slow plating rate and with a poor reduction yield, is carried out by stirring them with the water-soluble alkaline earth metal compounds and subsequent filtration. The excess of soluble alkaline earth metal compounds in the baths can be removed, if desired, by the addition of suitable precipitation agents. Thus, for example, an excess of Ca+ is suitably precipitated with oxalates, an excess of Ba++ with sulphates.

In a preferred way of carrying out this invention the working up of the chemical plating baths is effected continuously: during plating a supplementary metal salt solution and a solution of the reducing agent containing sodium hydroxide is continuously run into the plating bath in operation. The concentrations of both solutions are adjusted in such a way that the composition of the plating bath remains unchanged. By overflow, a quantity of bath liquid corresponding to the increase in volume is removed from the plating bath, and this, after regeneration and adjustment to the concentration of the supplementary metal salt solution, is again fed back into the plating bath.

The regeneration is carried out as follows: The overflow liquid is put into the circuit as an afterplating bath so that the residual reducing agent is used up. Subsequently a quantity of magnesium chloride is added which corresponds to the alkali metal and borate content of the solution; the mixture is filtered off from the precipitate, the residue is Washed with a little water, the filtrate is adjusted again to the concentration of the supplementary metal 'salt solution by the addition of metal salt and, if desired, of complex former.

As the interfering alkali metal salts are kept by the bath regeneration according to the invention at a concentration which does not influence the chemical plating process, it is possible to maintain the working capacity of a bath for a practically unlimited period of time. The

advantages of the working up of chemical plating baths according to this invention, which contain as reducing agent boron hydrides with one to four hydrogen atoms linked directly to boron, are as follows:

(1) It is possible to use these chemical plating baths continuously.

(2) The rate of deposition remains constant.

(3) The reduction yields remain constant.

(4) In the form of the water-soluble alkaline earth metal compounds, preferably magnesium chloride, a particularly easily accessible and very economical agent for the working up of the plating baths is available.

The following examples are given for the purpose of illustrating the invention:

Example 1 1 litre of a chemical plating bath of the composition Nickel chloride (NiCl .6H O) g./litre 30 Ethylene diamine (96-98%) g./litre 62 Sodium hydroxide g./litre 42 Thiodiglycollic acid g/litre 1 Lead chloride mg./litre 10 Sodium boranate mg./litre 0.6

is operated at 90 C. Four metal plates of an area of 1 sq. dm. per plate are introduced. The ratio metal surface [sq. c.]/ bath volume [cc.] equals 0.4. Every 30 minutes one plate is withdrawn from the bath and a new plate introduced, so that the immersion period of the first plate is 0.5 hours, the immersion period of the second plate 1 hour, the immersion period of the third plate 1.5 hours and the immersion period of each subsequent plate in the plating bath is 2 hours.

During this time 100 cc./ hour of a sodium borohydride solution of 12 g. NaBH in 1 litre 2 N sodium hydroxide solution and 100 cc./hour of a supplementary metal salt solution of Nickel chloride (NiCl .6H O) g./litre 118 Ethylene diamine g./litre 60 Thiodiglycollic acid g./litre 1 Lead chloride rng./litre 10 are continuously run in. I

100 cc. of the bath solution are withdrawn continuously per hour so that after a running period of 10 hours 1 litre of the sodium borohydride solution and 1 litre of the supplementary metal salt solution have been added to the plating bath. Evaporation losses amount to 1 litre in 10 hours when the plating vessel is open. During the same period 1 litre of liquid has been withdrawn from the plating bath and, after the working up and freshening up described below, is available as a new supplementary metal salt solution.

The working up of the bath liquid withdrawn is carried out in the following way:

(a) The reducing agent is removed from the bath by plating but can also be removed by treatment with magnesium salt.

(b) After determination of the content of alkali metal hydroxide and alkali metal borate a corresponding quantity of magnesium chloride (for example 100 g.

MgCl .6H O) is added as a solid or in a concentrated solution, while stirring, the mixture is filtered off from the precipitate and the residue washed with a little water.

The adjustment of the bath to the concentration of the supplementary metal salt solution can only be carried out by the addition of the nickel salt as a solid or in solution to the filtrate. The ethylene diamine content is equally adjusted to the initial concentration.

According to this instruction a bath was run for over 100 hours. Working up took place after every 10 hours running time. Working up losses of plating metal salt and complex former were small. When regenerating the bath after 40 hours plating time they amounted to 1.5 g./litre NiCl .6H O and 6 g./litre C H (NH after 80 hours plating time to 2.0 g./litre NiCl .6H O and 7 g./litre C H (NH In the plating bath a constant content of 80 to 90 g./litre NaCl was established. A total of 218 g. Ni- B-alloy was deposited. The rate of deposition amounted to about 10-12 ,u/hOlJI. The surfaces of the coated metal plates had a silvery appearance.

Example 2 Foils of polyglycol-terephthalate were consecutively pretreated in the following baths:

(a) 200 g. of sodium hydroxide+900 cc. of water and 0.5 g. of wetting agent.

Period of immersion minutes Temperature C 60 (b) 100 g./litre of stannous chloride+200 cc. of con- (c) 0.5 g./litre of palladium chloride-H0 cc./litre of concentrated hydroch oric acid.

Period of immersion minutes 5 Temperature C 20-30 Plating was carried out in a l-litre bath of the following composition:

Nickel sulphate g./litre 20 Cobalt sulphate g./litre 20 Concentrated aqueous ammonia cc./litre N-dimethylborazane g./litre 1.5 The temperature of the bath was 40 C., the period of immersion between 5 and 10 minutes. The bath was checked analytically and the initial concentration was re established every 5 hours. After about 20 hours running time the bath stopped plating. Regeneration was carried out by the addition of 50 g. of magnesium sulphate to the plating bath while stirring. Subsequently the precipitate formed was filtered off, the residue was washed with a little water and the filtrate was adjusted to the initial concentration of the plating bath by adding the metal salts, the complex former and the reducing agent. The bath now worked again without any disturbance. Silvery coatings were obtained on the polyglycol-terephthalate foils, with a resistance of between 0.4 and 0.6 ohm./ cm.

Example 3 2 litres of a chemical plating bath of the following compositions:

Cobalt chloride g./litre 45 Nickel chloride g./litre 10 Ammonium chloride g./litre 12 Tetraethyl ammoniumbromide g./litre 45 Concentrated aqueous ammonia cc./litre 160 Sodium borohydride of the plating salt was carried out by introducing dropwise 25 cc./hour of a solution of 320 g. cobaltous hexamine chloride in 1 litre 2 N aqueous ammonia. The plating bath was kept in motion by a slowly-running stirrer. The metal plates were replaced by new plates every six hours. The determination of the metal precipitate deposited was carried out by re-weighing the metal plates. Every 12 hours the plating bath was regenerated with calcium chloride. Working up was carried out by adding 20 g. of solid calcium chloride to the bath and stirring vigorously for 30 minutes. The precipitate was filtered off and the excess of calcium hydroxide in the filtrate was precipitated with an equivalent quantity of potassium oxalate. Filtration was repeated and the residue was washed with a little water. After a running period of 50 hours 20 g. of nickel chloride dissolved in 2 N aqueous ammonia were added to the bath. The bath was operated for over 101 hours without any noticeable change in the plating rate. After a plating period of 6 hours the precipitate on the six metal plates yielded a weight of deposited of 12.396 g., after 96 hours operation the weight on the six plates amounted to 11.942 g., after the same working time. The tot-a1 amount of cobaltous hexamine chloride added 'was 862 g., the total weight of metal deposited 208.3 g. The surfaces of the coated metal plates showed the typical dark lustre of cobalt coatings.

What is claimed is as follows:

1. In a process for regenerating a chemical plating bath containing as reducing agent a boron hydrogen compound having 1 to 4 hydrogen atoms linked directly with the boron atom, an alkali metal hydroxide or ammonia, a nickel and/or cobalt metal salt and a complex former selected from the group consisting of ammonia and organic complex forming agents, the step which comprises adding to the exhausted plating bath at least one water soluble alkaline earth metal compound selected from the group consisting of magnesium chloride, magnesium sulfate, magnesium acetate, calcium chloride, strontium chloride and barium chloride, and removing from the bath the precipitated borates and hydroxides thereby formed.

2. Process according to claim 1 wherein said Water soluble alkaline earth metal compound is added in the form of a solid.

3. Process according to claim 1, wherein said water soluble alkaline earth metal compound is added in the form of an aqueous solution thereof.

4. Process according to claim 1 wherein said alkaline earth metal compound is magnesium chloride.

5. Process according to claim 1 which comprises removing the excess of soluble alkaline earth metal compound in said bath by the addition to the bath of a suitable precipitating agent whereby the cationic fraction of said compound is precipitated and can be removed.

6. Process according to claim 5 wherein said soluble alkaline earth metal compound is a calcium compound and said precipitating agent is an oxalate.

7. Process according to claim 5 wherein said soluble alkaline earth metal compound is a barium compound and said precipitating agent is a sulfate.

8. In a process for the regeneration of a chemical plating bath containing as reducing agent a boron hydrogen compound having 1 to 4 hydrogen atoms linked directly to the boron atom, alkali metal hydroxide or ammonia, nickel and/ or cobalt metal salt and a complex former selected from the group consisting of ammonia and organic complex forming agents, the steps which comprise adding to the exhausted plating bath at least one water soluble alkaline earth metal compound selected from the group consisting of magnesium chloride, magnesium sulfate, magnesium acetate calcium chloride, strontium chloride and barium chloride, removing the precipitated borates and hydroxides thereby formed and adding to the bath liquid at least that amount of the bath components required to re-establish the initial content thereof in said bath.

References Cited UNITED STATES PATENTS 2,434,191 1/1948 Benner 204-52.l 2,886,451 5/1959 Budininkas 106-1 FOREIGN PATENTS 654,202 12/ 1962 Canada. 836,480 6/1960 Great Britain.

OTHER REFERENCES Kolthoif, S. M., et al. Textbook of Quantative Inorganic Analysis, 3rd ed., 1952, pp. 322-335 and pp. 337-351.

ALEXANDER H. BRODMERKEL, Primary Examiner. J. E. CARSON, -L. B. HAYES, Assistant Examiners. 

8. IN A PROCESS FOR THE REGENERATION OF A CHEMICAL PLATING BATH CONTAINING AS REDUCING AGENT A BORON HYDROGEN COMPOUND HAVING 1 TO 4 HYDROGEN ATOMS LINKED DIRECTLY TO THE BORON ATOM, ALAKI METAL HYDROXIDE OR AMMONIA, NICKEL AND/OR COBALT METAL SALT AND A COMPLEX FORMER SELECTED FROM THE GROUP CONSISTING OF AMMONIA AND ORGANIC COMPLEX FORMING AGENTS, THE STEPS WHICH COMPRISE ADDING TO THE EXHAUSTED PLATING BATH AT LEAST ONE WATER SOLUBLE ALKALINE EARTH METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM CHLORIDE, MAGNESIUM SULFATE, MAGNESIUM ACETATE CALCIUM CHLORIDE, STRONTIUM CHLORIDE AND BARIUM CHLORIDE, REMOVING THE PRECIPITATED BORATES AND HYDROXIDES THEREBY FORMED AND ADDING TO THE BATH LIQUID AT LEAST THAT AMOUNT OF THE BATH COMPONENTS REQUIRED TO RE-ESTABLISH THE INITIAL CONTENT THEREOF IN SAID BATH. 